What Makes an Excellent Short?

What makes an excellent short?

There's a difference between an excellent festival short and an excellent calling-card short, so I should be clear that in this post I'm talking about calling-card shorts.

I'm still trying to figure it out, but I think a good calling-card short would have to include:

-- Excellent cinematography, with at least a few flashy (yet appropriate) camera moves.

-- Excellent production values.

-- The appearance of costing a lot of money.

-- Pitch-perfect acting, without a single bad performance.

-- Snappy dialogue.

-- Some surprises in the narrative (though the "twist" ending has become cliché).

-- A story that grabs you by the balls or the funny bone (or both) and doesn't let go.

-- A brilliantly clever concept (George Lucas in Love and Troops come to mind, though that sort of self-referential stuff got clobbered by all the copycats that came along afterward).

Optional qualities would include:

-- A breakthrough in some area of technical filmmaking. (405, Prey Alone, Luxo Jr., etc.)

-- A twist on the general semiotics of filmmaking (La Jetee)

-- Nudity and/or sexuality that pushes the boundaries of what is accepted (this may not increase the quality of the short at all, but the movie will sure get passed around a lot more!).

-- Recognizable actors doesn't hurt (because it implies that you have the wherewithal to get recognizable actors to work for you).

...and for the kicker, all of that stuff should fit inside 15 minutes (or, even better, 10 minutes).

Of course, there are some excellent shorts that don't include several of these elements (like The Spirit of Christmas, which kickstarted the careers of the South Park guys), but I think the inclusion of all of those elements would drastically improve a short's chances.

For those of you who make shorts, which of these elements are missing? What can you do to change that?

For those of you who watch shorts (particularly if you watch them with an eye toward hiring good filmmakers), what other elements do you look for?